Drainage channels of this kind may be used to drain surfaces where the risk of contamination by soil, (scattered) sand or foliage is relatively slight, so that there is no absolute requirement for the interior of the channel to be readily accessible for cleaning.
For manufacturing such channels with a large nominal width (300 mm) and in large lengths (2 m), the previously known method is not suitable. In that method a core, which is provided to form the channel compartment, is constructed as a delicate hollow body made of sheet metal, within which are movably mounted a set of other cores to form the inlet openings. Such types of apparatus are not only extremely complicated and sensitive, but in addition the required high nominal widths and lengths cannot be produced.